The invention relates to an apparatus for encapsulating cells, more specifically, for encapsulating cells, such as animal cells, to form small capsules.
The encapsulation of living cells, such as animal cells including human cells, is of great significance in biotechnology and medicine, for example for immobilization purposes (see, for example, Uludag, H. et al., Advanced Drug Delivery Reviews 42 (2000), 29-64). For instance, body cells such as hepatocytes in microcapsules composed of ultrathin, semipermeable membranes can have applications, for example, in hybrid bioartificial liver-assisted devices. Such applications involve containment of encapsulated hepatocytes in a bioreactor that is implanted in patients with liver failure (see Chia et al., Tissue Engineering 6(5): 481-95). Another application is the encapsulation of islet cells for the production of insulin (see U.S. Pat. No. 5,462,866 for example). To mention a third example, erythropoetin producing kidney cells have been suggested for the treatment of anemia.
Encapsulation of cells in polymers, such as alginate, through an alginate-gelation complex coacervation method has been extensively studied. In this method, alginate, which is a glycuranan extracted from the brown seaweed algae, can be chelated by calcium to form a gel. Early results obtained with an alginate-polylysine system were inconsistent and thus inconclusive because of the uncontrollable purity of the alginate, and the incorporation of cells within the formed external membrane. Consequently, a two-step encapsulation scheme was used. The calcium alginate gel droplets were incorporated into larger alginate gel spheres and then reacted with a poly-amino acid such as poly-L-lysine to form a semi permeable membrane. Sodium citrate was then added to liquefy the interior to form microcapsules. Unfortunately, sodium citrate had adverse effect on the bioactivity of hepatocytes, and the water-soluble alginate and polylysine were found to be not particularly biocompatible as individual polymers. As a result, other alternatives, such as collagen, have been investigated to see if they are better substrates for cellular functions than alginate.
Manual encapsulation involves extrusion of a charged stream of cell mixture or suspension into an encapsulation solution of an opposite charge. Manual encapsulation works but the size of capsules produced is inconsistent and the process is time consuming.
U.S. Pat. No. 5,462,866 discloses an apparatus that is adapted to form microspheres by individually enveloping falling droplets of a polyanion solution with a collapsing annular sheet of a polycation solution while the sheet is traveling downwardly at the same velocity as the droplets. The apparatus includes an oscillator to produce the droplets and a means for deflecting a certain number of droplets to obtain an optimum ratio of polyanion droplets to polycation to produce uniform spheres.
U.S. Pat. No. 6,458,296 discloses a device that is adapted to divide an immobilization mixture into equal parts by superimposition of an external vibration. The device includes a metal ring having a through hole. The metal ring is mounted downstream from a nozzle with the nozzle axis extending through the through hole. The metal ring is connected to a high-voltage source that produces an electrical field between the metal ring and the nozzle. During use, an encapsulation mixture comprising an immobilization matrix and cells or substances is conveyed through the nozzle in such a way that a free laminar jet is produced. By virtue of a vibration being superimposed on the free jet, the free jet is broken up into drops of equal size. When the fluid penetrates into the electrical field, a charge flux occurs in the direction of the nozzle so that the separated drops have an electrostatic charge. This charge causes mutual repulsion of the drops. Consequently, the small radial displacements between the drops are increased and the single-strand chain of drops is expanded to form a cone of drops. These drops fall into a hardening bath to form particles. The charges of the drops are removed by grounding of the hardening bath.
U.S. Pat. No. 6,649,384 discloses a method and a system for the encapsulation of viable biological material with a polymeric material to form a gelled capsule, which preferably can be transplanted into genetically dissimilar hosts. The method includes an electrostatic mixing process for producing encapsulated cell clusters with at least two polymeric coatings. The system includes a spinning disc atomizer. Biological material is encapsulated in a first alginate layer and the resultant capsules are suspended in a liquid carrier medium such as a saline solution. An electrostatic charge is applied to the carrier medium which is then introduced into an alginate solution, and the resultant suspension is atomized and gelled to form a second alginate layer.
However, there remains a need for an alternative system that allows encapsulation of cells in a controlled, reproducible and economical manner.